A stator of a torque converter in an automatic transmission of a motor vehicle can rotate only in one direction by a one-way clutch, and a thrust load applied to the stator is supported by a thrust bearing. In the thrust bearing of the torque converter, a low friction is required for the purpose of reducing a loss of power energy transmission under a high speed driving condition so as to improve a specific fuel consumption. Accordingly, as this kind of thrust bearing, there has been employed a needle bearing, or a copper washer or the like. However, since the needle bearing and the copper washer are expensive, needs for a synthetic resin thrust bearing which can be inexpensively manufactured have been increased in recent years.
FIGS. 14A and 14B show a synthetic resin thrust bearing in accordance with a conventional art which is used in a torque converter or the like, in which FIG. 14A is a front view as seen from the side of a sliding surface, and FIG. 14B is a partly enlarged cross sectional view cut along a line XIV—XIV in FIG. 14A. As shown in the figures, in this kind of synthetic resin thrust bearing 100, a lot of lubricating grooves 102 extending in the radial direction are formed on a sliding surface 101 at a predetermined interval in the circumferential direction. Each of the lubricating grooves 102 is provided so as to supply a lubricating oil to the sliding surface 101, and groove shoulders 102a and 102b in both sides are formed as curved surfaces or chamfer portions having the same size.
However, in the conventional synthetic resin thrust bearing 100 shown in FIGS. 14A and 14B, since the lubricating oil introduced into the lubricating grooves 102 is hard to be sufficiently supplied to the lubricating surface 101, and further, since a depth d of the lubricating grooves 102 is shallow, a cooling effect achieved by the lubricating oil introduced into the lubricating grooves 102 is not sufficient. Furthermore, because of the above insufficiency, there have been pointed out problems such that a friction with an opposing sliding member is high, a performance of the torque converter is lowered, and the specific fuel consumption is increased.
The present invention is made by taking the problems mentioned above into consideration, and a technical object of the present invention is to provide a thrust bearing supporting a thrust load of a rotation portion, in which a friction with an opposing sliding member can be sufficiently lowered even when the thrust bearing is made of a synthetic resin.